In order to achieve good quality emissions from an internal combustion engine (i.e., fairly complete combustion of fuel with a low percentage emission of noxious substances in the engine exhaust), it is necessary to maintain the fuel injection pressure as high as possible. In most internal combustion engines which do not employ a common rail fuel injection system, the fuel injector comprises a translating plunger within the fuel injector body which is actuated by a camshaft that rotates in relation to the engine speed (usually at one-half engine speed). The camshaft operates upon a push rod which in turn moves a rocker lever that pushes on the plunger within the fuel injector, as is known in the art. At full-rated power, the internal combustion engine runs at a relatively high speed, which translates to a relatively high speed of the plunger within the fuel injector. This high-speed motion of the plunger in the fluid fuel creates extra injection pressure which helps to maintain emission quality. FIG. 1 illustrates a graph of fuel injection pressure versus engine RPM for a typical prior art internal combustion engine. It can be seen that at full-rated power (labeled RPM 2), the fuel injection pressure is relatively high at P.sub.SAC2.
As the speed of the engine decreases to the torque peak condition (labeled RPM 1), this speed-induced injection pressure decreases, lowering the total fuel injection pressure to P.sub.SAC1. Because of this lower fuel injection pressure, the quality of emissions produced by the engine also decreases at torque peak.
In order to improve the emission quality of the engine, it is therefore desirable to increase the fuel injection pressure created at torque peak conditions. The present invention is directed toward meeting this need.